Effect of Temperature on Wear Rate of Homopolar Pulse Consolidated Electrical Brush

Binderless copper-graphite composite electrical brushes are being developed using a high-energy, high-rate pulse sintering technique by the Center for Electromechanics at The University of Texas at Austin (CEM-UT). Experiments were done to investigate temperature's effect on the homopolar pulse consolidated (HPC) brush wear rate for an apparent brush current density of 180 A cm−2, a brush downforce of 44.5 N, and rotor surface sliding speeds of 10 m s−1 and 40 m s−1. At a sliding speed of 10 m s−1, it was found that brush wear rate dropped steeply as the brush bulk temperature increased from 80 °C to 103 °C. Other than this unusual wear finding in this particular sliding speed and temperature range, test results indicated that brush wear rate generally increased with increasing brush bulk temperature. At a sliding speed of 40 m s−1, it was found that brush wear rate suddenly increased by several times as the brush bulk temperature approached 149 °C. In the case of 10 m s−1 sliding speed, no stepwise rise in brush wear rate was observed even as the brush bulk temperature reached 156 °C.Center for Electromechanic

Homopolar Pipeline Welding, An Overview

Homopolar pulse welding (HPW) has been proposed as a one-shot, single stage welding process for the joining of pipe in the J-lay configuration. A joint industries program (JIP) has been formed to develop this process for off-shore, deep water applications. At this point, no studies have been conducted on the applicability of the method for underwater service, but its speed and lack of pressure sensitivity makes it an interesting possibility for future, deep water considerations. Homopolar pulse welding utilizes the high current, low voltage electrical pulse produced by a homopolar generator to rapidly resistance heat the interface between abutting pipe ends, producing a full circumference resistance forge weld requiring no filler metal in only three seconds. This five year program began in February 1993, funded by a consortium of six oil companies (Shell, Exxon, BP, Texaco, Amoco, and Mobil). The program's ultimate goal is to produce a prototype system suitable for installation on a barge. The goals for the first two years of the program include demonstrating suitability of the process by producing and evaluating welds in different grades and wall thicknesses of three inch nominal diameter API SL line pipe. Funding for each year of the program is contingent upon meeting program goals for the previous year.Center for Electromechanic

Homopolar Pulse Welding For Offshore Deep Water Pipelines

Homopolar pulse welding (HPW) is a one-shot resistance welding process being investigated as a method to join API SL carbon steel line pipe. Homopolar pulse welding utilizes the high current, low voltage electrical pulse produced by a homopolar generator to rapidly resistance heat the interface between abutting pipe ends, producing a full circumference resistance forge weld requiring no filler metal in under three seconds. A five year joint industry program is sponsoring HPW research with the goal of developing the process for deep water offshore pipeline construction utilizing the J-lay method. The first two years of the program have concentrated on weld parameter optimization by producing, testing, and evaluating welds in various grades, wall thicknesses, types and compositions of 3 inch nominal (3.S inch OD) diameter API SL carbon steel pipe. Mechanical properties of the welds and parent metal were evaluated by tensile testing, impact testing, and hardness traverse testing according to guidelines and criteria established by the industrial sponsors. Homopolar pulse welding has demonstrated the capability to produce industrially acceptable full circumference welds in carbon steel line pipe via a rapid, one-shot process. Future work will concentrate on developing the process for commercial field installation, with the program's goal being the demonstration of a prototype system for producing HPW welds in 12 inch diameter pipe in a J-lay configuration.Center for Electromechanic

Homopolar Welding for J-Lay Pipeline Construction

Homopolar Welding (HPW) is a high speed electric resistance forge welding process being developed for single shot girth welds proposed for the J-Lay pipelaying technique in deepwater. The homopolar welding technique uses the high amperage direct cmTent output from homopolar generators to produce localized heating at the pipe interface, completing a weld in under five seconds regardless of pipe diameter or wall thickness. During the most recent welding research program, homopolar pipe welding technology made substantial advances in the process using a laboratory fixture to join small diameter HSLA steel linepipe (3-inch Schedule 80). Specific improvements on two high strength linepipe steels (X60 & X65) include increased impact toughness to near base metal values, improved weld profile, near base metal microstructure at the weld, and reduced generator requirements. Based on these improvements, a new welding fixture was designed and built capable of joining 12 inch schedule 60 steel linepipe. Work is underway to adjust the operation of the new welding fixture to match the performance of the 3 inch welding fixture. Seven welds have been completed, all having base metal yield and tensile strengths and ductility. The paper will cover homopolar welding basics and the recently completed pipe welding research program, emphasizing the mechanical properties of welds and the robustness of the process.Center for Electromechanic

Homopolar Welding: Results of Five Years of Research

Homopolar welding (HPW) is a high speed electric resistance forge welding process being developed for single shot girth welds proposed for the J-Lay pipelaying technique in deepwater. The homopolar welding technique uses the high amperage direct current output from homopolar generators to produce localized heating at the pipe interface, completing a weld in under five seconds regardless of pipe diameter or wall thickness. During a recently completed five year welding research program, homopolar pipe welding technology made substantial advances in the process using a laboratory fixture to join small diameter HSLA steel linepipe (3-inch schedule 80). Specific improvements on two high strength linepipe steels (X60 & X65) include increased impact toughness to near base metal values, improved weld profile, near base metal microstructure at the weld, and reduced generator requirements. Based on these improvements, a new welding fixture was designed and built capable of joining 12-inch schedule 60 steel linepipe. Seven welds have been completed, all having base metal yield and tensile strengths and ductility. During the next major research program, adjustments to the operation of the 12-inch welding fixture will be implemented to match the performance of the 3-inch welding fixture and improve impact toughness in 12-inch welds. The paper will present the results of homopolar welding research for the past five years including specific modifications to the homopolar welding process.Center for Electromechanic

Homopolar Pulse Welding for Offshore Deep Water Pipelines

Homopolar Pulse Welding (HPW) is a one-shot resistance welding process being investigated as a method to join API 5L carbon steel line pipe. HPW utilizes the high current, low voltage electrical pulse produced by a homopolar generator to rapidly resistance heat the interface between abutting pipe ends, producing a full circumference resistance forge weld requiring no filler metal in under three seconds. A five year joint industry program is sponsoring HPW research with the goal of developing the process for deep water offshore pipeline construction utilizing the J-lay method. The first two years of the program have concentrated on weld parameter optimization by producing, testing, and evaluating welds in various grades, wall thicknesses, types and compositions of 3 inch nominal (3.5 inch OD) diameter API 5L carbon steel pipe. Mechanical properties of the welds and parent metal were evaluated by tensile testing, impact testing, and hardness traverse testing according to guidelines and criteria established by the industrial sponsors. HPW has demonstrated the capability to produce industrially acceptable full circumference welds in carbon steel pipe via a rapid, one-shot process

Advances in homopolar welding of API linepipe for deepwater applications

The University of Texas at Austin Center for Electromechanics is conducting a research program to study homopolar welding of line pipe for J-Lay applications. In 1995, the third year of the five year research program, process improvements increased Charpy V-Notch impact toughness properties to near parent metal values, while maintaining acceptable strength. After demonstrating repeatable performance, research focused on real world effects including evaluating the effect of poor fit up resulting from misalignment and rough and wavy interfaces. During the final year of the research program, the pipe welding program has scaled up to 12-inch nominal line pipe, a sevenfold increase in cross-sectional area. The paper will cover basics of homopolar welding, mechanical properties, weld upset profile, HPW metallurgy, and the studies of real world effects. Results from homopolar welding of 12-inch pipe will also be presented.Center for Electromechanic

Measurement and Prediction of Brush Interface Temperature at Sliding Electrical Contacts

Binderless copper-graphite composite electrical brushes have been fabricated with a high-energy and high-rate pulse sintering technique. Experiments were conducted to measure the interface contact spot temperatures of homopolar pulse consolidated brushes for a rotor surface sliding speed of 40 m/s, an apparent brush current density of 180 A/cm/sup 2/, and a brush down force of 44.5 N. Thermocouples were embedded in the brush samples at positions from 0.36 to 0.51 mm above the brush/rotor interface, and temperatures were monitored until the thermocouples were destroyed. Temperature readings of the thermocouples varied significantly as the interface approached. A three-dimensional finite-element thermal analysis for the homopolar pulse consolidated (HPC) brush contact spot was performed by using the heat input obtained from the experiments. The analytical results are in good agreement with the experimental data.Center for Electromechanic

Homopolar Pulse Welding: Characterization of Weld Parameters

This paper reports on the continuing research in homopolar pulse welding (HPW) as applied to pipe welding. As part of the NSF/Offshore Technology Research Center (OTRC). The program is designed to develop and commercialize this relatively new technology. The goal is to fully characterize the relative importance of the many coupled process variables and develop a real-time quality assurance system that will nondestructively determine the quality of a weld by simple electrical measurements. Potential commercial applications of HPW include large diameter pipe and other structures where a large cross-section must be welded quickly (i.e. laying of pipe with deep-sea lay barges, and construction of tension legs in the new deep-water tension leg drilling platforms) (Chung, 1985).Center for Electromechanic